Study On Squeeze Injection Technology Of Barium And Strontium Scale Inhibitors In West Of South China Sea Oilfield

In the process of water injection development in West of South China Sea Oilfield,the serious barium/strontium sulfate scales have occurred in the oil wells in the middle block of oilfield,due to the incompatibility between injected sea water with rich SO₄^2-and formation water with rich Ba²⁺and Sr²⁺.Many different methods of anti scaling have been tried during the period,the research results had a good scale inhibition effect on the scale of ground flow,but it can not prevent the formation of scale in the near well formation.In view of scaling in the near well formation,the downhole squeeze technology is an effective method for scale inhibition.Based on the scaling condition of western South China Sea Oilfield,downhole squeeze technology of scale inhibitor was studied in this paper,so as to provide some help for solving the scaling problem in oilfield.The basic performance evaluation of scale inhibitors was carried out according to the requirements of squeeze technology.A scale inhibitor 5^#was selected as an anti scaling agent,it had good chemical compatibility at 120℃,the inhibition efficiency in the range of5mg/L¹00mg/L was good and was basically unaffected by the value of pH,static inhibition efficiency could reach 90%;the scale inhibitor had good thermal stability at formation temperature.The adsorption experiments showed that the higher concentration of the scale inhibitor,the greater adsorption capacity was and it was greatly influenced by the pH value,when pH value was 4,the adsorption/desorption performance of scale inhibitor was the best.The design of squeeze process parameters for the target well were carried out.The design of squeeze process showed that the volume of preflush slug was 25m³,the size of scale inhibitor slug was 36m³ and the volume of overflush slug was 120m³,the radius of the front of overflush was r_o=2.79m and the radius of the front of scale inhibitor was r_s=3.18m.In addition,the mathematical model of squeeze life prediction was established and the software for predicting the life was developed.The results of model verification showed that the software was in good agreement with measured data of the well,which proved the accuracy of the software.Using the software to predict the squeeze life of the optimized scale inhibitor,the results showed that the minimum effective concentration had a great influence on the life,the lower the minimum effective concentration was,the longer the squeeze life was.